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Am Fam Physician. 2001;63(12):2427-2435

The prevalence of asthma and obesity has been increasing in the United States and throughout the world during the past 15 years. Several studies have noted a direct correlation between body mass index (BMI) and asthma. However, it is unclear whether asthmatics are more sedentary, which results in weight gain, or if obesity somehow increases the risk of developing asthma. There is some evidence that losing weight improves pulmonary function and oxygenation in obese patients, but the consequence of decreasing BMI on asthma severity is unknown. Hakala and colleagues attempted to clarify the effect of weight loss on various measures of pulmonary function such as peak expiratory flow (PEF) rate in patients with asthma.

Adult asthmatics between 25 and 62 years of age who had a BMI in the moderate to morbid obesity range (32.5 to 42.5 kg per m2) were enrolled in the study. All patients had stable disease and were using maintenance inhaled corticosteroids. Some patients were taking theophylline or a long-acting beta2 agonist, but none were cigarette smokers. Baseline PEF measurements, pulmonary function tests and asthma severity scores (specifically, dyspnea and cough) were measured. The participants were then placed on a weight reduction program that used a very-low-calorie diet preparation offering 1,760 kilojoule per day for eight weeks. No changes were made in their asthma therapy, except for rescue therapy with beta2 agonists. The patients recorded the highest of three PEF measurements each morning and evening for 14 successive days before and after the weight loss period.

Fourteen patients were enrolled in the study, including 11 women and three men. The mean weight loss was 13.7 kg (30.1 lb), and the BMI decreased by 5.1 kg per m2. There was a significant improvement in morning and evening PEF values in patients who had weight loss. The mean difference between the highest and the lowest morning PEF values decreased by 38 percent after weight reduction, and there was a significant decrease in day-to-day PEF variation. The mean forced expiratory volume in one second (FEV1) before weight loss was 77 percent of predicted, and the forced vital capacity (FVC) was within the normal range. Weight reduction produced a significant improvement in both parameters. There was an increase in airflow rate at low lung volumes (mean forced expiratory flow during the middle of forced vital capacity [FEF25–75%]). Significant increases were also noted in functional residual capacity and expiratory reserve volume, with the latter increasing from 0.43 L to 0.72 L. Regarding the symptom scores, a significant decrease in dyspnea was noted, but no decrease in cough was noted.

The authors conclude that in asthmatic patients weight loss produces a decrease in airway obstruction and PEF variability and improves asthma symptoms. These findings suggest that obesity may thus increase the degree of airway obstruction in patients with this chronic pulmonary disease.

editor's note: Intuitively the results of this study do not seem surprising. However, from a counseling and prevention standpoint, these results definitely provide physicians with yet another reason to encourage overweight patients, with and without asthma, to lose weight.—j.t.k.

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